JP5552884B2 - Manufacturing method of wheel bearing rolling bearing unit - Google Patents

Description

  The present invention relates to an improvement in a method of manufacturing a wheel-supporting rolling bearing unit for rotatably supporting a wheel with respect to a suspension device of an automobile, and relates to a wheel-supporting rolling bearing unit that is lightweight and has sufficient durability. The realization of the resulting manufacturing method is intended.

  In order to rotatably support the wheel with respect to the automobile suspension system, a wheel bearing rolling bearing unit 1 as shown in FIG. 4 is used. In this wheel support rolling bearing unit 1, a hub 3 is rotatably supported via a plurality of rolling elements 4, 4 on the inner diameter side of an outer ring 2. Out of these, the outer ring 2 is made of medium carbon steel, and has double-row outer ring raceways 5 and 5 on the inner peripheral surface and a stationary flange 6 on the outer peripheral surface. Such an outer ring 2 does not rotate when the stationary flange 6 is coupled and fixed to the knuckle constituting the suspension device when used. The hub 3 has double-row inner ring raceways 7 and 7 and a rotation side flange 8 on the outer peripheral surface, and rotates with a wheel coupled and fixed to the rotation side flange 8 in use. Each of the rolling elements 4 and 4 is made of bearing steel or ceramic and is provided between the outer ring raceways 5 and 5 and the inner ring raceways 7 and 7 so as to be freely rollable in both rows. ing. In addition, the rotating flange 8 supports and fixes a braking rotator such as a wheel and a disc rotor in use.

  The hub 3 is formed by connecting and fixing a hub body 9 and an inner ring 10. Of these, the hub main body 9 is made of medium carbon steel, and is a portion near the outer end in the axial direction (outside with respect to the axial direction means the side that is the outer side in the width direction of the vehicle body when assembled to the suspension device. The same applies to the entire claims.) The rotation-side flange 8 is directly attached to the outer peripheral surface of the inner ring raceway, and the axially outer inner ring raceway 7 of the double row inner ring raceways 7 and 7 is directly attached to the outer peripheral surface of the axial direction. Forming. A cylindrical portion 11 called a pilot portion is provided at the outer end of the hub body 9 in the axial direction for positioning the wheel and the braking rotator. A recess 12 is formed at the center of the axially outer end surface of the hub body 9 at the axially outer end of the hub body 9 including the inner diameter side of the cylindrical part 11.

  On the other hand, the inner ring 10 is made of bearing steel and has an outer circumferential surface on the inner side in the axial direction of the double-row inner ring races 7 and 7 (inner with respect to the axial direction is the center in the width direction of the vehicle body when assembled to the suspension device). The inner ring raceway 7 is formed, which is the same in the entire specification and claims. Such an inner ring 10 is caulked 14 formed at the inner end in the axial direction of the hub body 9 in a state where the inner ring 10 is externally fitted and fixed to a small-diameter step 13 formed near the inner end of the hub body 9 in the axial direction. The hub body 9 is coupled and fixed to the hub body 9. A structure in which a nut is screwed to a male screw portion provided at an axially inner end portion of the hub body 9 in order to connect and fix the inner ring 10 to the hub body 9 is also widely known.

  In any structure, a part of the hub 3 is quenched and hardened. First, the entire inner ring 10 is cured by so-called submerged quenching in which the entire inner ring 10 is heated and immersed in quenching oil. On the other hand, with respect to the hub main body 9, the hardened layer 15 is formed in the portion shown by the oblique lattice in FIG. 5 by quenching and hardening by high-frequency heat treatment. This hardened layer 15 is a portion closer to the outer diameter of the intermediate portion of the hub body 9 (surface layer portion including the outer peripheral surface), and from the proximal end portion on the inner side in the axial direction of the rotation side flange 8 to the small diameter step portion 13. It is formed in the part hung on the outer half in the axial direction. By forming the hardened layer 15 in such a portion, the moment rigidity of the rotation side flange 8 is ensured, the rolling fatigue life of the inner ring raceway 7 on the outer side in the axial direction is ensured, and the fretting wear of the small diameter step portion 13 is achieved. And to secure the bending rigidity of the hub body 9 as a whole. The concave portion 12 opened on the outer end surface in the axial direction of the hub body 9 contributes to weight reduction of the hub body 9.

When the wheel supporting rolling bearing unit 1 including the hub body 9 as described above is used, a large force (load) is applied to the hub 3. In particular, during turning, a large moment is applied to the rotation side flange 8 from the contact portion between the wheel supported and fixed to the rotation side flange 8 and the road surface. Such a moment is supported by a continuous portion 16 between the base end portion (inner diameter side end portion) of the rotation side flange 8 and the main body portion of the hub main body 9. The thickness of the continuous portion 16 is not only originally small due to the presence of the concave portion 12, but also based on the presence of the hardened layer 15, the thickness of an unquenched (so-called raw) portion that is easy to ensure toughness. Is small. For this reason, unless any measures are taken, it is impossible to achieve both weight reduction by increasing the volume of the concave portion 12 and securing the strength and rigidity of the continuous portion 16.

For this reason, conventionally, it has been considered to improve the strength, rigidity and durability of the hub body by means such as those described in Patent Documents 1 to 4, for example. Of these, Patent Document 1 describes a technique for securing the strength of the hub body by subjecting the hub body to a tempering treatment. Further, Patent Document 2 discloses that a crack is caused by removing the decarburized layer on the inner surface of the recess to make the inner surface smooth, and further generating residual compressive stress on the inner surface by shot peening or turning, and starting from the inner surface. The technique which makes it hard to generate | occur | produce damages, such as this, is described. Patent Document 3 describes a technique for forming a protrusion projecting radially inwardly on the inner peripheral surface portion of the recess to improve the strength and rigidity of the peripheral portion of the recess. Further, in Patent Document 4, the inner surface portion of the recess is cooled at the end of the forging process for manufacturing the hub body, and a layer of a non-standard structure such as a fine ferrite / pearlite structure is formed on this portion. Techniques for improving the strength and fatigue life of the steel are described.

  In the case of the prior art described in Patent Documents 1 to 4 as described above, it is possible to obtain a certain effect, but from the aspect of securing the durability of the hub body 9 while suppressing the cost and further reducing the weight. The present inventors have found that there is room for improvement. That is, in the conventional techniques described in Patent Documents 1 to 4, in consideration of cost reduction, cracks are likely to occur in the continuous portion 16 in the hub body 9 as the hardened layer 15 is processed. It cannot be prevented. That is, due to the study by the present inventors, a large residual tensile stress is generated in the inner diameter side portion existing on the radially inner side of the hardened layer 15 including the continuous portion 16 as the hardened layer 15 is processed, It was found that the cracks are likely to occur. This point will be described with reference to FIG.

  When the intermediate portion in the axial direction of the outer peripheral surface of the hub body 9 is induction-quenched and then rapidly cooled to form the hardened layer 15, the portion that should become the hardened layer 15 rapidly shrinks after thermal expansion. As a result, residual compressive stress is applied to the hardened layer 15 as shown in FIG. On the other hand, a residual tensile stress is applied to the inner diameter side portion of the hub body 9 that is present on the radially inner side of the hardened layer 15. That is, the inner diameter side portion rises in temperature with heat conduction during heating for induction hardening, while the temperature drop during the rapid cooling is delayed as compared with the portion to be the hardened layer 15. And when the said inner diameter side part shrink | contracts with a temperature fall, the said hardened layer 15 has already been formed, and this hardened layer 15 becomes resistance with respect to the said inner diameter side part thermally contracting. This inner diameter side portion is thermally contracted against the resistance caused by such a hardened layer 15, and as a result, residual tensile stress is applied to the inner diameter side portion. Of these stresses, the residual compressive stress acts as a force that suppresses crack damage, while the residual tensile stress acts as a force that promotes this damage.

  In this way, when residual tensile stress is applied to the inner diameter side portion and a stress in the tensile direction is applied to the portion in accordance with the moment, crack damage is caused in the hub body 9 starting from the inner diameter side portion. It tends to occur. FIG. 6 is a modified Goodman diagram showing a situation in which crack damage is likely to occur due to the residual tensile stress acting in this manner. In FIG. 6, a solid line α represents a Goodman line, and a broken line β represents a yield line. Assuming that the stress amplitude is a predetermined value (constant) and the average stress becomes a tensile stress starting from point a where the average stress is 0, the combination of this average stress and the stress amplitude is the upper side of the Goodman line α. Especially, as shown by point B in FIG. 6, there is a high possibility that the crack damage will occur beyond the yield point. Further, the crack damage due to such a cause becomes significant when the volume of the recess 12 is increased (the depth in the axial direction is increased) in order to further reduce the weight of the hub body 9.

The conventional techniques described in Patent Documents 1, 3, and 4 among the aforementioned Patent Documents 1 to 4 cannot suppress crack damage due to such a cause. In contrast, the conventional technique described in Patent Document 2 can suppress crack damage due to such a cause, but it is necessary to newly add a shot peening or turning process. In shot peening, a hard layer with a very thin surface becomes a compressive stress, but a strong tensile stress is generated directly under the hard layer, and the internal origin may break. Furthermore, in order to perform these shot peening or turning processes, equipment completely different from the equipment for heat treatment is required, the cost required for capital investment increases, and the manufacturing cost of the wheel bearing rolling bearing unit increases. This will cause the problem.
Further, in the prior art described in Patent Document 5, when the intermediate portion in the axial direction of the outer peripheral surface of the hub body 9 is induction-quenched, the inner diameter side is cooled with cooling water. A technique for suppressing crack damage is disclosed. However, for cooling water, facilities such as temperature control and management of the contact area of the cooling water are required, and drying equipment is also required to prevent rusting, which increases the manufacturing cost of rolling bearing units for supporting wheels. Will end up.

JP 2005-3061 A JP 2005-145313 A JP 2006-143069 A JP 2007-38804 A JP 2010-084887 A

  In view of the circumstances as described above, the present invention can be implemented at low cost, and is present on the radially inner side of the hardened layer as a hardened layer is formed by induction hardening on the outer peripheral surface of the intermediate portion of the hub body. The present invention has been invented to realize a method for manufacturing a wheel bearing rolling bearing unit capable of reducing the value of the residual tensile stress generated in the inner diameter side portion.

A wheel-supporting rolling bearing unit that is an object of the manufacturing method of the present invention includes an outer ring, a hub, and a plurality of rolling elements.
Among these, the outer ring has a double row outer ring raceway on the inner peripheral surface, and does not rotate during use.
The hub has a double-row inner ring raceway on the outer peripheral surface, and rotates together with the wheel when in use. The hub main body and the inner ring are coupled and fixed. Of these, the hub body directly forms the rotation side flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and the inner ring raceway on the outer side in the axial direction on the outer peripheral surface in the axial direction. A recess is formed in the central portion of the outer end surface in the axial direction. The inner ring is formed with an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and is fitted and fixed to a small-diameter step portion formed near the inner end in the axial direction of the hub body. A hardened layer is formed by induction hardening at least on the outer peripheral surface of the intermediate portion of the hub body including the inner ring raceway on the outer side in the axial direction.
Further, a plurality of rolling elements are provided between the outer ring raceways and the inner ring raceways so as to be freely rollable in both rows.

In order to manufacture such a wheel-supporting rolling bearing unit, the manufacturing method of the wheel-supporting rolling bearing unit of the present invention devises the processing process of the hub body. And the value of the residual tensile stress which generate | occur | produces in the internal diameter side part which exists in a radial inside rather than the said hardened layer is suppressed small. That is, in the case of the invention described in claim 1 of the manufacturing method of the wheel supporting rolling bearing unit of the present invention, after forming the hardened layer, the inner surface of the concave portion is annealed by high frequency heating. The heating temperature at this time is about 600 to 650 ° C. when the hub body is medium carbon steel containing 0.4 to 0.7 mass% of C as in the invention described in claim 1 . Further, by setting the depth of heating to 600 to 650 ° C. during the annealing to 40% or less of the thinnest portion of the hub body, the portion heated to 600 to 650 ° C. is formed in the cured layer. Do not reach.
Further, in the case of the invention described in claim 2 of the manufacturing method of the rolling bearing unit for supporting a wheel according to the present invention, after the hardened layer is formed, the rotating flange or the base end of the rotating flange is formed. Or while cooling both, the inner surface of the recess is annealed by high frequency heating.

According to the method for manufacturing the wheel-supporting rolling bearing unit of the present invention having the above-described configuration, a hardened layer is formed on the outer peripheral surface of the intermediate portion of the hub body by induction hardening, and the inner diameter side of the hardened layer is formed. It is possible to reduce the value of the residual tensile stress generated in the inner diameter side portion. As a result, cracking damage to the hub body starting from the inner diameter side portion can be made difficult to occur.
Furthermore, the equipment necessary for carrying out the manufacturing method of the wheel bearing rolling bearing unit of the present invention having the above-described configuration is basically a high-frequency coil for heating the inner diameter side. For this reason, it is possible to make crack damage to the hub main body less likely to occur at a significantly lower cost than other conventionally known methods.

  That is, in the case of the method for manufacturing a wheel-supporting rolling bearing unit according to the present invention, the inner diameter side portion softens as the temperature rises due to high frequency heating, and the metal structure of the inner diameter side portion moves based on the residual tensile stress. (This inner diameter side portion is deformed). As a result, the residual tensile stress in the inner diameter side portion is relaxed (value is reduced).

Moreover, as a material of the hub main body used in the manufacturing method of the wheel bearing rolling bearing unit of the present invention, medium carbon steel is preferable. Medium-carbon steel can be plastically processed by rolling, forging, and press forming in addition to cutting such as grinding and turning, and then necessary parts can be hardened by induction hardening and rolling. The required performance as a bearing unit can be exhibited. Specifically, it is preferable to use a medium carbon steel containing 0.3 to 0.8% by mass of carbon (C) in terms of carbon content. More preferably, as in the invention described in claim 1, a medium carbon steel containing 0.4 to 0.7% by mass of carbon is used. If the carbon content is 0.3% or less, the required performance as a rolling bearing unit, for example, the required hardness may not be obtained even by high-frequency heat treatment, and if it exceeds 0.8 mass%, plastic working is easy. May be lost. In the case where the rough manufacturing process of the hub body is in the order of plastic working, high-frequency heat treatment, and cutting, the plastic processing property and the appropriateness of the hardening treatment by high-frequency heat treatment are taken into consideration . In addition, the carbon content is preferably 0.4 to 0.7% by mass. Most preferably, S45C to S55C of carbon steel for machine structure defined by JIS is used.

  Further, the inner diameter side portion softens as the temperature rises due to high frequency heating, which is the main part of the method of manufacturing the wheel bearing rolling bearing unit according to the present invention, and the inner diameter side portion metal is based on the residual tensile stress. The action of the movement of the structure (the inner diameter side portion is deformed) is most preferably exhibited in carbon steel having a carbon content of 0.4 to 0.7% by mass. The effect that the tensile stress is relaxed (value is reduced) is most preferably obtained.

  FIG. 1 shows an example of an embodiment of the present invention. In the case of this example, first, a hardened layer 15 (see FIG. 5) is formed by induction hardening at a portion near the outer diameter including the outer peripheral surface at the axially intermediate portion of the hub body 9. In the formation of the hardened layer 15, first, the energization (not shown) of the high frequency induction heating coil disposed around the axially intermediate portion of the hub body 9 causes the axially intermediate portion of the hub body 9 to The portion near the outer diameter including the outer peripheral surface is heated. Next, the hub body 9 is rapidly cooled to form the hardened layer 15 near the outer diameter. Such an induction hardening process for forming the hardened layer 15 is the same as a conventionally known induction hardening process, and therefore illustration and detailed description thereof are omitted.

Along with such induction hardening, a large residual tensile stress is generated in the inner diameter side portion including the continuous portion 16 existing on the radially inner side of the hardened layer 15 as described above. Therefore, following the operation of forming the hardened layer 15, as shown in FIG. 1, on the rotating side, a part of the hub body 9 is energized to the high frequency induction heating coil 17 disposed inside the recess 12. After heating the inner diameter side portion including the continuous portion 16 of the base end portion of the flange 8 and the main body portion of the hub body 9 to about 600 to 650 ° C., the inner diameter side portion is gradually cooled and annealed. At this time, the portion reaching 600 to 650 ° C. is prevented from reaching the hardened layer 15 . In general, in the case of the hub body 9 that is usually used well, the maximum depth of the hardened layer 15 is 1 to 5 mm, and the thickness of the thinnest portion of the hub body 9 (for example, the hub shown in FIG. 5). 60% or less of the A part) in the main body 9. Therefore, the portion reaching 600 to 650 ° C. is set to 40% or less of the thickness of the thinnest portion in the hub body 9 . Incidentally, more preferably 30% or less, and most preferably 20% or less. Moreover, if it shows with a dimension roughly, after heating the site | part about 0.1-4 mm in depth from the surface of the inner diameter side part to 600-650 degreeC, it is preferable to cool and anneal gradually.

  By annealing the inner diameter side portion including the continuous portion 16 in this manner, the residual tensile stress of the inner diameter side portion is relaxed (value is reduced). That is, the inner diameter side portion softens as the temperature rises due to high frequency heating based on energization of the high frequency induction heating coil 17, and the metal structure of the inner diameter side portion moves based on the residual tensile stress (the inner diameter side portion is Deform. In short, the metal structure of the inner diameter side portion moves based on the residual tensile stress, and the value of the residual tensile stress decreases along with the movement. As a result, as the hardened layer 15 is formed on the outer peripheral surface of the intermediate portion of the hub body 9 by induction hardening, the value of the residual tensile stress generated in the inner diameter side portion existing on the inner diameter side of the hardened layer 15. It is possible to suppress crack damage of the hub body 9 starting from the inner diameter side portion.

  Furthermore, in the case of this example, as a facility for suppressing the occurrence of crack damage of the hub body 9, a high-frequency induction heating coil 17 necessary for heating the inner surface of the recess 12 is sufficient. The heating depth and temperature can also be adjusted by adjusting the output and frequency. In particular, when the recesses are made deeper and deeper to reduce weight, and in order to increase the moment stiffness of the bearings, they are arranged in double rows as shown in FIG. When the rolling elements have different diameters PCD1 and PCD2 (PCD1> PCD2) and have a different diameter PCD, and the recesses can be made deeper and deeper, the hardened layer on the raceway surface has a tempering temperature. If it is set to (for example, 200-250 degreeC), it can be combined with a tempering process. The high-frequency induction heating coil 17 may be small, and the power supply equipment may be shared with the high-frequency induction heating coil for forming the hardened layer 15. For this reason, equipment required to reduce the residual tensile stress can be obtained at low cost, and an increase in manufacturing cost can be suppressed as compared with the case of the prior art described in Patent Document 2 described above.

An experiment conducted for confirming the effect of the present invention will be described. The experiment was conducted on the outer peripheral surface of the intermediate part with respect to the hub body 9 made of medium carbon steel (carbon content 0.4 to 0.7% by mass) as shown in FIGS. 2 (A) to (D). After forming the hardened layer 15 (see FIG. 5) by high-frequency heating and rapid cooling in the portion, know the effect of high-frequency heating and annealing the inner surface of the recess 12 on the magnitude of the stress remaining on the inner surface of the recess 12 I went for it. In this experiment, the measurement position of the residual stress was the part indicated by the arrow in FIG. All of the four types of hub main bodies 9 are for ordinary passenger cars, and the inner diameter of the opening of the cylindrical portion 11 surrounding the recess 12 is 48 mm. Further, the rotation-side flange 8 formed on the outer peripheral surface near the outer end in the axial direction has a cross shape as shown in FIG. In FIGS. 2A to 2D, the aspect ratio and the radius of curvature of the curved surface are drawn in accordance with the actual situation (according to the actual proportion). In the annealing step, the inner surface of the recess 12 was heated to 600 to 650 ° C. and held for 5 to 20 seconds, and then cooled by air at a rate of about 20 to 100 ° C./sec. Water cooling may be used, but air cooling is preferably used because air cooling is simpler in terms of facilities and the like.
In addition, when combined with the tempering step as described above, the cooling is performed only in the recess 12, and the cooling rate is the cooling rate in the recess 12.

この表１に示した実験結果から明らかな通り、本発明の車輪支持用転がり軸受ユニットの製造方法によれば、ハブ本体９の中間部外周面に硬化層１５を形成するのに伴ってこの硬化層１５の径方向内側に存在する内径側部分に発生した引っ張り応力を、表面だけでなく、焼鈍した深さまで緩和乃至は解消できる。 The results of experiments conducted under such conditions are shown in Table 1 below. In Table 1, the residual stress value of “+” represents tensile stress. In the annealing column, “No” represents the state before annealing after forming the hardened layer 15, and “Yes” represents the state after further annealing after forming the hardened layer 15. Yes.

As is apparent from the experimental results shown in Table 1, according to the method for manufacturing the wheel-supporting rolling bearing unit of the present invention, this hardening is accompanied with the formation of the hardening layer 15 on the outer peripheral surface of the intermediate portion of the hub body 9. The tensile stress generated in the inner diameter side portion existing on the radially inner side of the layer 15 can be reduced or eliminated not only on the surface but also on the annealed depth.

The rolling bearing unit manufacturing method of the present invention is such that the four flanges 8 of the form shown in FIG. 3 are independently formed in a cross shape as in the invention described in claim 5 or It is suitable for manufacturing a rolling bearing unit including a hub body having a so-called star-shaped flange formed of five or more, particularly for mass production. That is, in the preferred embodiment of the method for manufacturing a rolling bearing unit according to the present invention, the recess 12 is heated by high-frequency heating and then cooled by air cooling. Even if there is a portion or the like, the concave portion 12 which is the inner surface corresponding to the portion can be processed uniformly. Also, the equipment necessary for obtaining the effects of the present invention is relatively low cost. Therefore, even in the so-called mass production process, the rolling bearing unit having the effects of the present invention can be manufactured stably and at low cost.

  In order to obtain the effect of the present invention more efficiently, it is preferable to form the cross-sectional shape of the recess 12 provided in the hub body 9 smoothly. More preferably, there is no ridge (corner), and even more preferably, the bottom (the end in the axial direction of the recess 12) has an arc shape. By making the cross-sectional shape of the recess 12 smooth, heating by high frequency and subsequent air cooling become more uniform on the inner surface of the recess 12, so that the rolling can stably exhibit the effects of the present invention. The manufacturing method of a bearing unit can be implemented.

  In the hub body 9, the hardness of the portion other than the hardened layer 15 (non-hardened portion) including the recess 12 is preferably Hv145 to 400. If it is less than Hv145, the strength of the flange 8 or the like may be insufficient, and if it exceeds Hv400, the reliability with respect to an impact load or the like may be impaired.

Here, in order to set the hardness of the non-cured portion including the concave portion 12 to Hv 145 to 400, the hub body 9 has a carbon content of 0.4 to 0.7 mass% as in the invention described in claim 1. It is preferable to form a basic shape by cold forging from medium carbon steel. By work hardening by cold forging with respect to medium carbon steel having a carbon content of 0.4 to 0.7 mass%, the hardness of the non-hardened portion can be relatively easily set to Hv 145 to 400. Further, the carbon content is 0.3 to 0.8% by mass, preferably , as in the invention described in claim 1, formed by 0.4 to 0.7% by mass of medium carbon steel by cold forging. The concave portion 12 can maintain the Hv of 145 to 400 by high-frequency heating and subsequent cooling of the concave portion 12 according to the present invention. In this case, the base end portion of the rotary side flange 8 and the rotating-side flange 8 to work hardening by cold forging, so as not to deleted reducing the strength improvement effect based on work hardening, the invention described in claim 2 Similarly, it is preferable to perform high-frequency heating of the concave portion 12, which is a feature of the present invention, while cooling the rotation-side flange 8, the base end portion of the rotation-side flange 8, or both. Cold forging is suitable for so-called mass production processes, and the cost reduction effect can be obtained as the quantity increases.

  That is, in consideration of the invention specific matters, operational effects, embodiments, etc. of the present invention described so far, the rolling bearing unit manufacturing method of the present invention has a carbon content of 0.4 to 0.7% by mass of medium carbon. It is suitable as a method for manufacturing a rolling bearing unit having a hub having a cross-shaped or star-shaped flange shape formed by cold forging steel.

  The present invention can be applied to a case where the hub body is manufactured by cold forging, and a particularly remarkable effect can be obtained. The reason for this is that cold forging has a large processing resistance, and a large residual stress is likely to be generated inside the hub body produced by cold forging. That is, if a residual tensile stress generated along with the formation of a hardened layer is applied to a hub body that originally has a large residual stress, damage such as a crack is likely to occur. Therefore, when the present invention is applied to a hub body manufactured by such cold forging, it is possible to effectively prevent damage. However, even in the case of warm forging or hot forging, although there is a difference in degree, residual stress is generated inside the hub body to be produced, so it is effective to apply the present invention.

Sectional drawing which shows the implementation condition of this invention typically. Sectional drawing of four types of hub main bodies used for the experiment conducted in order to confirm the effect of this invention. The figure which looked at the hub main part of (C) of Drawing 2 from the right side of the figure. Sectional drawing which shows one example of the rolling bearing unit for wheel support used as the object of the manufacturing method of this invention. The half part sectional view for demonstrating the residual stress which generate | occur | produces in a hub main body accompanying hardening layer formation. The diagram for demonstrating the reason the durability of a hub main body falls with generation | occurrence | production of a residual tensile stress. The figure explaining what is called a "different diameter PCD hub unit".

DESCRIPTION OF SYMBOLS 1 Rolling bearing unit for wheel support 2 Outer ring 3 Hub 4 Rolling body 5 Outer ring raceway 6 Stationary side flange 7 Inner ring raceway 8 Rotation side flange 9 Hub body 10 Inner ring 11 Cylindrical part 12 Recessed part 13 Small diameter step part 14 Caulking part 15 Hardening layer 16 Continuous Part 17 High-frequency induction heating coil

Claims (5)

An outer ring having a double row outer ring raceway on the inner peripheral surface and not rotating even when used, a hub having a double row inner ring raceway on the outer peripheral surface and rotating together with the wheels during use, both the inner ring raceways and the both outer rings A plurality of rolling elements that are provided in a freely movable manner between the raceways, and the hub is a hub made of medium carbon steel containing 0.4 to 0.7 mass% of C. The main body and the inner ring are connected and fixed. Of these, the hub main body has a rotating flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and the outer periphery of the intermediate portion in the axial direction. The inner ring track on the outer side in the axial direction is directly formed on the surface, and the concave portion is formed on the central portion of the outer end surface in the axial direction. The inner ring is formed on the outer peripheral surface with the inner ring track on the inner side in the axial direction. The hub body is externally fitted and fixed to a small-diameter step formed on the axially inner end portion of the hub body. A method of manufacturing a wheel-supporting rolling bearing unit in which a hardened layer is formed by induction hardening on at least a portion including the inner ring raceway on the outer side in the axial direction on the outer peripheral surface of the intermediate portion of the hub body, after forming the layer, by high-frequency heating an inner surface of the recess, and annealed at 600 to 650 ° C., the depth of heating during the annealing 600 to 650 ° C., the thinnest portion among the hub main body 40 %, The portion heated to 600 to 650 ° C. is prevented from reaching the above-mentioned hardened layer . An outer ring having a double row outer ring raceway on the inner peripheral surface and not rotating even when used, a hub having a double row inner ring raceway on the outer peripheral surface and rotating together with the wheels during use, both the inner ring raceways and the both outer rings A plurality of rolling elements are provided between the raceway and each row, and the hub is formed by coupling and fixing the hub body and the inner ring. The hub body directly forms the rotation side flange for supporting and fixing the wheel on the outer peripheral surface near the outer end in the axial direction, and the inner ring raceway on the outer peripheral surface in the axial direction on the outer peripheral surface in the axial direction. A concave portion is formed in the central portion of the outer end surface, and the inner ring is formed by forming an inner ring raceway on the outer peripheral surface on the inner side in the axial direction, and a small-diameter step portion formed near the inner end in the axial direction of the hub body. The hub body is fitted and fixed at least on the outer peripheral surface of the intermediate portion of the hub body. A portion including an inner ring raceway of the axially outer, a manufacturing method of a wheel support rolling bearing unit which forms the hardened layer by induction hardening, after the formation of the hardened layer, the rotation side flange or the rotation A method for manufacturing a wheel-supporting rolling bearing unit, characterized in that the inner surface of the recess is annealed by high-frequency heating while cooling the base end of the side flange or both . The wheel support according to any one of claims 1 to 2 , wherein a hardness of an uncured portion other than the cured layer including the inner surface of the concave portion in the hub body is Hv145 to 400. A method for manufacturing a rolling bearing unit. The hub body is separated from the carbon steel material in containing C 0.4 to 0.7% by weight, shaping the basic shapes by cold forging, according to any one of claims 1 to 3 Of manufacturing a wheel support rolling bearing unit. The shape of the rotation-side flange, which forms a cruciform four flanges independently or any one of claims 1 to 4, a star shape form which is formed by five or more 1 The manufacturing method of the rolling bearing unit for wheel support described in the term.

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